1. Field of the Invention
The present invention relates to a method of processing data, and more particularly, to processing data in a Medium Access Control (MAC) layer.
2. Discussion of the Related Art
FIG. 1 is a structural diagram illustrating an Universal Mobile Telecommunication System (UMTS) network of a conventional mobile communication system. The UMTS is comprised of, largely, a user equipment (UE), a UMTS Terrestrial Radio Access Network (UTRAN), and a core network (CN). The UTRAN comprises at least one Radio Network Sub-systems (RNS), and each RNS is comprised of one Radio Network Controller (RNC) and at least one base station (Node B) which is controlled by the RNC. In each Node B, there is at least one cell.
FIG. 2 is a diagram illustrating a structure of a Radio Interface Protocol (RIP) which is located between a UE and the UTRAN. Here, the UE is associated with a 3rd Generation Partnership Project (3GPP) wireless access network standard. The structure of the RIP is comprised of a physical layer, a data link layer, and a network layer on the horizontal layers. On the vertical plane, the structure of the RIP is comprised of a user plane, which is used for transmitting data, and a control plane, which is used for transmitting control signals. The protocol layers of FIG. 2 can be categorized as L1 (first layer), L2 (second layer), and L3 (third layer) using an Open System Interconnection (OSI) modes as the basis.
L1 uses the physical channel to provide Information Transfer Service (ITS) to the higher layer. The physical layer is connected with the MAC layer via a transport channel through which data between the two layers is transmitted. As for transmitting data between the transmitting side and the receiving side, data is transmitted via the physical channel.
In L2, the MAC is connected with the RNC via a logical channel through which the MAC provides service to the RNC. Here, the MAC can be further defined by a plurality of sub-layers, such as MAC-b, MAC-c/sh, MAC-d, MAC-e, based on the transmission channels.
FIG. 3 is a diagram illustrating protocol of an Enhanced Dedicated Channel (E-DCH). As illustrated in FIG. 3, the MAC-e sub-layer, which supports the E-DCH, is located below the UTRAN and the MAC-D sub-layer of the UE, respectively. The MAC-e sub-layer of the UTRAN is located in Node B and in each UE. On the other hand, the MAC-d sub-layer of the UTRAN is located in the Serving RNC (SRNC) and in each UE.
As discussed above, the MAC layer comprises the MAC-d sub-layer, MAC-es sub-layer, and the MAC-e sub-layer. With respect to a UE, there is more than one data channel which can transmit data simultaneously, and each data channel is endowed with different service qualities. Here, the service quality refers to data error ratio and transmission delay time, for example, and follows independent service quality parameter for each data channel. In other words, for example, if there are a voice service and an internet service, since the parameters for providing each service is different, the settings for the downlink channels transmitting data are different.
Furthermore, the data rate transmitted through each channel is not constant, and the data rate changes with time. For example, in a wireless communication system, one E-DCH can be allocated to a UE, and subsequently, if only one data channel can be mapped to the E-DCH at a specified time, data transmission efficiency would decrease and wireless channel resources would be wasted. In detail, assume that the E-DCH has a capability to transmit 1000 bits of data at a specified time. In this example, a first E-DCH designated data channel has 500 bits of data at the specified time, and a second E-DCH designated data channel has 300 bits of data at the same specified time. If one E-DCH designated data channel, which can transmit 1000 bits of data at a given time, is used to transmit 800 bits of data instead of using two different channels to transmit the same amount of data, inefficient utilization of data channel can be minimized while reducing waste of unnecessary wireless resources.
To promote efficiency of wireless communication resources, every time data passes through each sub-layer of the MAC-d/MAC-es/MAC-e, data blocks of each higher layer can be combined to form a lower layer data block. In this case, the transmitting end has to provide the receiving end information on identifying the higher layer data block so that the receiving end can accurately identify and separate a plurality of higher layer data blocks from the lower layer data block. Such information is referred to as mapping information.
Although providing detailed description of the data block combinations in the mapping information helps the receiving end to separate the data blocks, providing too much information can actually be more harmful. That is, because the mapping information is not data but control information, and therefore, providing too much control information can clog the transmission channel and waste valuable resources. Furthermore, the mapping information should minimize using the lower channels (e.g., transport channels) so that the receiving end can more accurately separate the data blocks. In other words, the mapping information should be comprised of very small number of bits or should use least amount of lower channel resources while carrying maximum amount of data.